1. Field of the Invention
The invention relates to a method for forming a surface mounted device (SMD)-type piezoelectric vibrator in which a piezoelectric vibrating reed is sealed in a cavity formed between two bonded substrates, a piezoelectric vibrator manufactured by the manufacturing method, and an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.
2. Description of the Related Art
Recently, a piezoelectric vibrator utilizing quartz or the like has been used in cellular phones and portable information terminals as the time source, the timing source of a control signal, a reference signal source, and the like. Although there are various piezoelectric vibrators of this type, a surface mounted device-type piezoelectric vibrator is known as one example thereof. As the main piezoelectric vibrator of this type, generally, a three-layered piezoelectric vibrator in which a piezoelectric substrate having a piezoelectric vibrating reed formed thereon is interposed between the base substrate and a lid substrate from above or below is known. In this case, the piezoelectric vibrating reed is accommodated in a cavity (sealed space) that is formed between the base substrate and the lid substrate.
Moreover, in recent years, instead of the three-layered piezoelectric vibrator, a two-layered piezoelectric vibrator has also been developed. The piezoelectric vibrator of this type has a two-layered structure in which a base substrate and a lid substrate are directly bonded, and a piezoelectric vibrating reed is accommodated in a cavity formed between the two substrates. The two-layered piezoelectric vibrator is ideally used, as it is superior for achieving a thin profile compared with the three-layered structure, and the like.
Meanwhile, when the two-layered piezoelectric vibrator is manufactured, a method in which a base substrate and a lid substrate are anodically bonded using a bonding film formed on the lower surface (bonding surface) of the lid substrate is known. Specifically, the two substrates superimposed on each other with a bonding film disposed therebetween, for example, are set on an electrode substrate of an anodic bonding machine, and a predetermined bonding voltage is applied between the bonding film and the electrode substrate. In this way, it is possible to cause an electrochemical reaction to occur at the interface between the bonding film and the base substrate. As a result, the bonding film and the base substrate are closely adhered tightly, and the base substrate and the lid substrate are anodically bonded.
As a piezoelectric vibrator of this type, a configuration disclosed in Patent Document 1 as below is known. The piezoelectric vibrator includes an airtight container in which a planar lid member (lid substrate) and a planar base member (base substrate) are superimposed on each other in the thickness direction; a piezoelectric vibrating reed which is provided in the airtight container; extraction electrodes which are provided on the superimposed surface (bonding surface) of the lid member and are electrically connected to the piezoelectric vibrating reed through connection portions and in which the connection portions are extended to edge portions of the superimposed surface of the lid member; outer electrodes which are electrically connected to the extraction electrodes from the side surfaces of the airtight container; and a bonding film which is formed of metal or silicon and is provided between the superimposed surface of the lid member and the superimposed surface of the base member. Moreover, in the piezoelectric vibrator, an insulating film is provided at least between the extraction electrodes and the bonding film among the portions between the superimposed surface of the lid member and the superimposed surface of the base member.
According to the piezoelectric vibrator having such a configuration, since the extraction electrodes and the bonding film are electrically isolated by the insulating film, it is possible to prevent conduction between the extraction electrodes, and to apply a voltage to the piezoelectric vibrating reed through the outer electrodes.    Patent Document 1: JP-A-2007-89117
However, the piezoelectric vibrator of the related art and the manufacturing method thereof have the following problems.
First, although the bonding film used for anodic bonding is formed by photolithography, since the apparatus needed for the photolithography is expensive, there is a problem in that bonding the lid member and the base member by anodic bonding incurs a large cost.
Another problem is that the insulating film needs to be provided between the extraction electrodes and the bonding film, which requires lots of time and labor. A further problem is that since it is preferable that the surface of the insulating film be flat in order to perform reliable anodic bonding, much more time and labor is required to planarize the insulating film.
The invention has been made in view of the above problems, and an object of the invention is to provide a two-layered surface mounted device-type piezoelectric vibrator which can be manufactured easily and at a low cost and a method for manufacturing the piezoelectric vibrator. Moreover, another object of the invention is to provide an oscillator, an electronic device, and a radio-controlled timepiece each having the piezoelectric vibrator.